The entire disclosure of Japanese Patent Application No. 2007-020881, filed Jan. 31, 2007 is expressly incorporated herein by reference.
1. Technical Field
The present invention relates to a flushing method that may be used in a liquid ejecting apparatus such as an ink-jet printer and the like. More specifically, the present invention to a flushing method that senses when the nozzles of the liquid ejecting apparatus have become sufficiently unclogged.
2. Related Art
A liquid ejecting apparatus includes a liquid ejecting head that is capable of ejecting liquid in the form of liquid drops. Using this configuration, a liquid ejecting apparatus is capable of ejecting various kinds of liquid from its liquid ejecting head. One example of a liquid ejecting apparatus is an image recording apparatus such as an ink-jet printer, although there are other types of liquid ejecting apparatuses. An ink-jet printer performs a recording process by discharging liquid in the form of ink drops from nozzles that are provided on the recording head toward an ink discharge target medium or target object such as recording paper or the like. When the discharged ink drops land on the surface of the ink discharge target medium, dots are formed, forming an image.
In addition to the image recording apparatus mentioned above, there are various other types of liquid ejecting apparatuses used in the art today including a those used to produce the color filters of liquid crystal display devices.
A typical image recording apparatus stores ink in a liquid reservoir, such as an ink tank, ink cartridge, or the like. As the ink enters a pressure generation chamber in the recording head, a driving signal is applied to a pressure generation source, such as a piezoelectric vibration element or the like, causing a pressure change to the ink contained in the pressure generation chamber. The pressurized ink then is discharged from the apparatus as ink drops from a plurality of nozzles. Thus, the liquid is ejected by controlling the pressure of the recording head. Moreover, the recording head is configured to increase or decrease the amount of liquid (i.e., weight and volume) discharged as ink drops from the nozzles by varying the driving voltage, that is, by controlling the electric potential difference between the minimum voltage and the maximum voltage supplied to the pressure generation source as a driving signal.
Typically, liquid ejecting apparatuses of the related art perform a flushing process before starting a printing job, during the printing job, and/or after the completion of the print job by discharging liquid k that has become thickened from inside the nozzles. Thus, the flushing process is performed to each nozzle provided on the recording head clean and unclogged. By this means, it is possible to consistently discharge the desired amount of ink drops from each nozzle, effectively preventing any missing dots. One example of one such flushing process of the related art is described in Japanese Patent Application JP-A-2006-123499.
In the typical flushing processes of the related art, the number of times that ink is discharged during the flushing process is determined based on “worst case” ink viscosity conditions. For example, in many processes it is assumed that three or four months have elapsed since the last ink was discharged from the nozzles. In other words, the flushing operation flushes the nozzles enough times to prevent any nozzle from clogging, even those nozzles where the ink is in the worst condition. For example, all of nozzles are set to discharge ink drops approximately 5,000 times during the flushing process. In these configurations, however, a large amount of ink drops are unnecessarily discharged because the ink has not thickened yet, resulting in a considerable amount of waste. On the other hand, if the ink has thickened beyond the predetermined “worst case” scenario, it is practically impossible, or at least very difficult to effectively clean the clogged nozzles using the predetermined number of the flushing operations, posing another problem that has not yet been addressed by the related art.
In particular, pigmented ink, which has excellent color reproduction qualities, tends to thicken easily because it is manufactured by dispersing pigment in an ink solvent with a high volatility. Thus, the pigment ink is prone to clogging the nozzles. Accordingly, it is necessary to perform flushing operations more frequently for the pigmented ink. In response to the increased number of flushing operations, however, there is a demand for reducing the amount of wastefully discharged ink during the flushing operations because the pigmented ink is expensive.